Method for the production of hydrogen-containing gaseous mixtures

ABSTRACT

A method for the production of a hydrogen-containing gas composition, such as a synthesis gas including hydrogen and carbon monoxide. The molar ratio of hydrogen to carbon monoxide (H 2 :CO) in the synthesis gas can be well-controlled to yield a ratio that is adequate for the synthesis of useful products such as methane or methanol, without the need to remove carbon oxides from the gas stream to adjust the ratio.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/771,163, filed on Feb. 3, 2004, which is a continuation applicationof U.S. patent application Ser. No. 10/178,889, filed on Jun. 24, 2002,now U.S. Pat. No. 6,685,754, which is continuation-in-part of U.S.patent application Ser. No. 10/085,436, filed on Feb. 28, 2002, now U.S.Pat. No. 6,663,681, which is a continuation-in-part of U.S. patentapplication Ser. No. 09/800,769. filed Mar. 6, 2001, U.S. patentapplication Ser. No. 09/800,423 filed Mar. 6, 2001, U.S. patentapplication Ser. No. 09/800,421 filed Mar. 6, 2001 and U.S. patentapplication Ser. No. 09/800,434 filed Mar. 6, 2001, now U.S. Pat. No.6,620,398. Each of the foregoing is incorporated herein by reference intheir entirety.

STATEMENT REGARDING FEDERALLY FUNDED RESEARCH

None

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a method for the production ofvaluable hydrocarbon products by reacting a carbonaceous material andsteam in a molten metal to form a synthesis gas that can be used toproduce high-value hydrocarbon products. More particularly, the presentinvention is directed to a method for the production of a synthesis gasthat includes a controlled ratio of hydrogen to carbon monoxide bycontacting a carbonaceous material and a reactive metal with steam,wherein a portion of the steam reacts with the carbonaceous material anda portion of the steam reacts with the reactive metal. The synthesis gascan be used to form high-value hydrocarbon products, such as methane ormethanol.

2. Description of Related Art

Recently, the United States and other countries have experienced ashortage of natural gas and as a result, natural gas prices forconsumers have increased substantially. Accordingly, there is a pressingneed for economic methods for the manufacture of a high-value heatinggas that can be used in place of natural gas. Natural gas has acomposition that includes from about 80 percent to 93 percent methane(CH₄), the balance including ethane (C₂H₆), propane (C₃H₈), butane(C₄H₁₀) and nitrogen (N₂). Methane, the primary component of naturalgas, has a heating value of about 21,520 Btu/lb. Thus, an economicmethod for the production of methane would supplement the use ofnon-renewable natural gas.

There are many natural resources in addition to natural gas that areutilized to produce energy. For example, coal can be burned inconventional boilers to generate steam, which is converted to energythrough steam turbines. 85 percent of the electricity in the UnitedStates is generated by combusting fossil fuels, namely coal, oil andnatural gas. Coal however, because of its high carbon content, generateslarge quantities of carbon dioxide (CO₂), and the use of coal forelectricity generation is a major contributor to the 5.5 billion tons ofCO₂ emitted by the United States per annum. The 5.5 billon tons of CO₂amounts to one-fourth of the world emissions. Coal combustion is alsoresponsible for other pollution, most notably sulfur dioxide (SO₂) andnitrogen oxides (NO_(x)), both of which are now regulated.

Furthermore, only 30 percent of the heat generated by burning coal isconverted into electricity and 70 percent is wasted to the atmosphere.In contrast, electrical generation in modern plants burning natural gasis about 50 percent efficient and natural gas produces only about 60percent of the CO₂ that coal produces.

As an alternative to simply burning high carbon containing materials,such as coal, the materials can be converted to a synthesis gas in agasifier. Synthesis gas includes five major gaseous components—carbonmonoxide (CO), hydrogen (H₂), methane, carbon dioxide and steam (H₂O).These gases are derived from the carbon (C), hydrogen, and oxygen (O₂)molecules found in the high carbon containing material and steam used toconvert the high carbon containing material to synthesis gas. Otherelements, designated impurities, typically found with carbonaceousmaterials include sulfur (S), nitrogen (N₂), chlorine (Cl₂) and fluorine(F). These impurities can form minor amounts of other gaseous species.Taken together the major and minor gases constitute a “raw” synthesisgas stream. As used herein, synthesis gas refers to the gas mixtureafter the minor gases have been removed. Nitrogen, steam and carbondioxide do not contribute to the heating value and therefore typicallyare reduced or eliminated from the gas stream. The term “syngas” refersto a gaseous mixture that includes only hydrogen and carbon monoxide.

Synthesis gas has numerous applications, including the conversion of thesynthesis gas into valuable hydrocarbons. In one application, thesynthesis gas can be converted to methane, which is burned in a combinedcycle power plant to generate electricity. The combined cycle gasturbines can be located at coal-fired generating stations thereby takingadvantage of existing coal-handling infrastructure and electricaltransmission lines. Most importantly, compared to coal-fired electricalgenerators, the conversion efficiency of thermal to electrical energyincreases by about 67 percent. Concomitantly, there is a reduction incarbon dioxide emissions per unit of electricity.

For a gas turbine, gas is input to the turbine and the output is thermalenergy. For increased efficiency, a gas with a high thermal energy percubic foot is desirable. The net heating value (heat of combustion) ofthe three major components of synthesis gas are illustrated in Table 1below. These values assume that the heat contained in the steam, thecombustion product of hydrogen, is not recovered. TABLE 1 Net Heats ofCombustion Synthesis Gas Component Btu/lbs Btu/ft³ Carbon Monoxide 4,347322 Hydrogen 51,623 275 Methane 21,520 913

As is illustrated in Table 1, methane releases more than three times theamount of heat that hydrogen releases on a per cubic foot basis. Thereason for this is that hydrogen occupies more cubic feet on a per poundbasis, even though hydrogen has more Btu on a per pound basis. Due toits clean burning nature and high heat content, methane is the preferredfuel. Consequently, syngas (H₂ and CO) is more economically burned afterit is converted to methane.

Syngas can be used to form other hydrocarbons in addition to methane.Since 1955, SASOL, a South African entity has been producing a waxysynthetic crude from syngas. Some transportation fuel, about 11 percentgasoline, is extracted from the synthetic crude. However, due to thelarge portion of hydrocarbons having a high molecular weight andoxygenated organics that are also produced, other approaches have beeninvestigated for making specific materials from syngas.

There are well known processes for producing methanol (CH₃OH) and aceticacid (CH₃COOH) from syngas, for example. Typically, methanol is producedusing syngas derived from natural gas, which exerts further pressure onthe price and availability of natural gas. At least one major US oilcompany has developed a family of catalysts that produce a mixture ofhydrocarbons in the gasoline range with high selectivity from methanol.Because methanol can be readily made from syngas, and catalysts areavailable for converting methanol into gasoline with great selectivity,coal-derived syngas affords the US an opportunity to achieve energyindependence.

Methanol is also a chemical building block for manufacturing a widearray of other products, including: MTBE (methyl tertiary butyl ether)used in reformulated gasoline; formaldehyde resins, used in engineeredwood products and products such as seat cushions and spandex fibers;acetic acid used to make PET (polyethylene terepthalate) plastic bottlesand polyester fibers; and windshield wiper fluid. Additionally, methanolis relatively environmentally benign, is less volatile than gasoline andis a leading candidate to power fuel cell vehicles.

There are known processes for converting coal into gaseous products.Hydrogasification converts coal and steam into a raw synthesis gas.Gasification, a companion process, employs coal, steam and oxygen andproduces hydrogen, carbon monoxide and carbon dioxide, but no methane.Pyrolysis, which utilizes heat alone, partitions coal into volatilematter and a coke or char. The volatile matter includes hydrogen,oxygen, some portion of the carbon (volatile carbon), organic sulfur andtrace elements. The coke or char includes the balance of the (fixed)carbon and the ash derived from the mineral matter accompanying theorganics.

Heat by itself disproportionates gaseous volatile matter, derived fromcoal, into methane and carbon as is illustrated by Equation 1.CH_(x)→(x/4) CH₄+[1−(x/4)]C   (1)

-   -   (where the value of x must be less than 4)

The hydropyrolysis reaction combines hydrogen and volatile matter toform methane and carbon. This reaction, illustrated by Equation 2, isexothermic.CH_(x)+m H₂→[(x+2m)/4]CH₄+{1−[(x+2m)/4]}C   (2)

-   -   (where the sum of x plus 2m must be less than 4)

The following solid-gas chemical reactions are applicable to thehydrogasification of organics at temperatures above 1200° C. The highlyexothermic reaction of carbon and oxygen illustrated by Equation 3 canbe a primary source of process heat, producing about −394 MJ/kg-mole ofheat.2 C+O₂→2 CO   (3)

The hydrogasification of carbon is also an exothermic reaction,illustrated by Equation 4, yielding −75 MJ/kg-mole of heat.C+2 H₂→CH₄   (4)

The steam-carbon reaction illustrated by Equation 5, is highlyendothermic, requiring +175 MJ/kg-mole of heat.C+H₂O→CO+H₂   (5)

Gas phase reactions, applicable to the formed fuel gases at temperaturesbelow 1000° C. include the mildly exothermic (2.8 MJ/kg-mole) water gasshift reaction, illustrated in Equation 6.CO+H₂O→H₂+CO₂   (6)

The highly exothermic methanation reaction is illustrated in Equation 7(−250 MJ/kg-mole).CO+3 H₂→CH₄+H₂O   (7)

Gasification is the process step that converts a solid (or liquid) fuelinto a gaseous fuel by breaking (disassembling) the fuel into itsconstituent parts (molecules). When gasified with steam and oxygen,organic material is converted into a synthesis gas that may include fivegaseous components: carbon monoxide, hydrogen, methane, carbon dioxideand steam.

The concentration of the individual product gases (all reactions above)all move in the direction of thermodynamic equilibrium, limited bykinetics, which is strongly related to temperature. The temperature ofthe gasifier, therefore, is the predominate factor that determines whichgaseous species will form and in what amount. FIG. 1 illustrates theinfluence of temperature on a mixture of gases (four parts hydrogen andone part each carbon monoxide and methane) allowed to come tothermodynamic equilibrium. This mixture was thermodynamicallyequilibrated at various temperatures, over a range from 200° C. to 1200°C. In addition to temperature, the type of gasifying equipment (movingbed, fluidized bed or entrained flow) also exerts a strong influence onthe resulting synthesis gas mix.

Equation 8 illustrates the ideal coal hydrogasification reaction.Coal+H₂O →CH₄+CO₂   (8)

The ideal hydrogasification reaction illustrated by Equation 8 isslightly endothermic and is favorable for methane production only at lowtemperatures, where the kinetics are too slow to be commercially useful.To circumvent this thermodynamic dilemma, various hydrogasificationprocesses have been proposed for coal. These processes conduct asequence of related chemical reactions such that the sum of thereactions is identical to the ideal reaction of Equation 8. One sequenceof reactions includes gasification to convert the solid fuel, coal orother organic material, into a gaseous fuel by reacting it with steamand usually oxygen at high temperatures and in an entrained flowgasifier. This gasification step produces a gas comprised predominantlyof hydrogen and carbon monoxide, with some impurities. Typically, theresulting ratio of hydrogen to carbon monoxide (H₂:CO) for entrainedflow reactors falls between 0.5 and 0.8. The water gas shift reactioncan be used to increase the ratio of hydrogen to carbon monoxide bysubtracting carbon monoxide from the system. This is done by reactingcarbon monoxide with additional steam to produce carbon dioxide. Sulfurand other impurities can also be removed from the raw synthesis gas. Theresulting carbon dioxide can be removed by pressure swing adsorption oramine scrubbing. Finally, the scrubbed syngas, with the proper H₂:COratio, is passed over appropriate catalysts to produce, for example,methane (3:1 ratio) or methanol (2:1 ratio).

The H₂:CO ratio produced by other gasifying systems varies, as shownbelow in Table 2. (Data taken from Perry's Chemical Engineers' Handbook,7^(th) ed, 1997, Table 27-11) TABLE 2 Gasifying Systems COMMERCIALGASIFYING SYSTEM H₂:CO RATIO Moving Bed Type Lurgi 1.77 BG Lurgi 0.58Fluid Bed Type KRW (Air) 0.63 KRW (Oxygen) 0.51 Entrained Flow Shell0.42 Texaco 0.77

The H₂:CO ratio for the above gasifiers is less than 1.9. The Lurgigasifying process has the highest H₂ to CO ratio, however, it can onlyutilize coal in the size range of 2 mm to 50 mm. The resultingrequirement for disposal of material smaller than 2 mm imposes anonerous economic burden on the Lurgi process. An example of a gasifierhaving a rotatable grate is disclosed in U.S. Pat. No. 3,930,811, byHiller et al. The H₂:CO ratios for all other gasifiers listed in Table 2is less than 1. These ratios are established primarily by the reactortype and the type of coal. This fixed ratio, unique to eachgasifier-coal combination, occurs because all of the gasifiers above useoxygen to supply adequate input heat to secure a process heat balancefor a specified coal and steam rate. Any change in coal rate or steamrate, for the intended purpose of affecting the H₂:CO ratio, woulddestroy the heat balance. Prabhakar G. Bhandarkar in an articleentitled. Gasification Overview Focus on India, Hydrocarbon Asia,November/December 2001, discusses various gasification systems includingsome of those listed in Table 2.

Molten metal gasification is one technique for gasifying coal. Anexample of a molten metal gasification process is disclosed in U.S. Pat.No. 4,389,246 by Okamura et al. issued Jun. 21, 1983 and assigned toSumitomo Metal Industries. Okamura et al. discloses an example(Example 1) wherein coal and steam was fed into a furnace containingmolten iron at 1500° C. The coal was fed at a rate of 3.5 tons per hourand the steam was fed at a rate of 400 kg/hr (0.44 tons/hr). The steamand coal were blown onto the surface of the molten metal along withoxygen at high velocities to produce a depression of a specifiedgeometry. The average gas production was 7500 Nm³/hr. The actualcomposition of the gas as reported by Okamura et al. was: CarbonMonoxide 62.5% Hydrogen 33.9% Oxygen 0.02% Nitrogen  1.4% Carbon Dioxide 2.0% Total Sulfur <80 ppm

The Okamura et al. example is typical of oxygen-blown slagginggasifiers. The critical parameter from the example is the H₂:CO ratio,which is only 0.54:1 (33.9/62.5). In contrast, a 3:1 or 2:1 ratio isnecessary to produce methane or methanol, respectively.

In addition to the Okamura et. al. patent there are other knownprocesses for producing synthesis gas from steam and carbon. Forexample, U.S. Pat. No. 1,592,861 by Leonarz discloses a method for theproduction of water gas (primarily H₂ and CO) by contacting steam withuncombined carbon in a bath of molten metal. The steam is dissociatedinto its constituent elements by carburetion at temperatures of 900° C.to 1200° C. The carbon combined with the oxygen of the gas is sufficientin quantity to produce carbon monoxide but not to make an appreciablequantity of carbon dioxide.

U.S. Pat. No. 2,953,445 by Rummel discloses the gasification of fuelsand decomposition of gases in a molten slag bath. It is disclosed that awater gas composition is obtained composed primarily of hydrogen andcarbon monoxide wherein the ratio of hydrogen to carbon monoxide isabout 0.38:1.

U.S. Pat. No. 4,187,672 by Rasor discloses an apparatus for convertingcarbonaceous material into fuel gases. For example, raw coal can begasified in a molten metal bath such as molten iron at temperatures of1200° C. to 1700° C. Steam is injected to react with the carbonendothermically and moderate the reaction.

U.S. Pat. No. 4,388,084 by Okane et al. discloses a process for thegasification of coal by injecting coal, oxygen and steam onto molteniron at a temperature of about 1500° C. A gas product is produced havinga ratio of hydrogen to carbon monoxide of about 0.5:1.

U.S. Pat. No. 5,645,615 by Malone et al. discloses a method fordecomposing carbon and hydrogen containing feeds, such as coal, byinjecting the feed into a molten metal using a submerged lance.

Donald B. Anthony, in a 1974 Thesis entitled “Rapid Devolatilization andHydrogasification of Pulverized Coal,” found that rapid heating of coalin the presence of hydrogen can increase the amount of volatile mattersignificantly. Under thermal decomposition, different chemical bondsrupture at different temperatures. The rupturing bonds release volatilesand initiate char-forming reactions. Short-lived (<1 second)intermediaries in the char-forming sequence can react with hydrogen toform additional volatile matter. It was also found that freshlydevolatilized coal is more reactive than pretreated coal. Further, thecarbon that is residual from freshly devolatilized coal may possessexcess free energies. The equilibrium constant for the hydrogasificationreaction may be larger by a factor of 10 or more.

A significant limitation of the foregoing methods for producing syngasis that the synthesis gas must be treated to remove carbon oxides beforethe gas product can be used to produce high-value products such asmethane or methanol. Process steps to eliminate carbon oxides from thegas stream are relatively costly. It would be advantageous to provide amethod that can provide a synthesis gas having a controlled ratio ofhydrogen to carbon monoxide, and in particular where the molar ratio ofhydrogen to carbon monoxide is at least about 1:1, such as at leastabout 2:1, for the subsequent formation of high-value hydrocarbons.

BRIEF SUMMARY OF THE INVENTION

According to one embodiment, the present invention provides a method forthe conversion of a carbonaceous material, such as coal, into a valuablesynthesis gas that can be converted to high-value hydrocarbons such asmethane or methanol. The ratio of hydrogen to carbon monoxide in thesynthesis gas can be well controlled to enable the economical productionof hydrocarbons, such as methane or methanol.

The present invention allows coal, an abundant resource, to be convertedto synthesis gas, which is then available for conversion to cleanburning methane and methanol, thereby relieving demand on the naturalgas supply and reducing CO₂ emissions. Also, synthesis gas from coalaccording to the present invention can serve as the basic component fromwhich synthetic gasoline can be manufactured.

According to one embodiment of the present invention, a method isprovided for the production of a gas stream including hydrogen andcarbon monoxide wherein the molar H₂:CO ratio is at least about 1:1. Themethod includes the steps of providing a molten metal in a reactor thatincludes at least a first reactive metal, contacting steam with thereactive metal to react a first portion of the steam with the reactivemetal and form hydrogen gas and a metal oxide and contacting acarbonaceous material with the molten metal in the presence of steam toreact the carbonaceous material with a second portion of the steam andform carbon monoxide gas. A gas stream can be extracted from the reactorwhich has a molar H₂:CO ratio of at least about 1:1, such as at leastabout 2:1.

According to another embodiment of the present invention, a method forthe production of a gas stream including hydrogen and carbon monoxide isprovided wherein the H₂:CO molar ratio is at least about 1:1. The methodincludes providing a molten metal in a reactor including at least afirst reactive metal, contacting steam with the molten metal to react afirst portion of the steam with the reactive metal to form hydrogen gasand a metal oxide, contacting a carbonaceous material with the moltenmetal to react the carbonaceous material with a second portion of thesteam and form carbon monoxide, extracting a gas stream from the reactorhaving a molar H₂:CO ratio of at least about 1:1. After a period oftime, the steam flow is terminated and the metal oxide is reduced with areductant back to the metal. By operating two such reactors in parallel,a gas stream containing H₂ and CO can be produced substantiallycontinuously.

According to another embodiment of the present invention, a method forthe gasification of coal is provided. The method includes the steps ofinjecting coal into a molten metal contained a reactor, injecting steaminto the molten metal and extracting a gas stream from the reactorincluding hydrogen and carbon monoxide wherein the molar ratio of H₂:COis at least about 1:1. A sufficient excess of steam is injected into themolten metal to react the first portion of the steam with the coal andform carbon monoxide and to react a second portion of the steam with themolten metal to produce hydrogen gas and a metal oxide.

The present invention is also directed to a method for the production ofhydrocarbon products. According to one embodiment, a method for theproduction of methane gas is provided. The method includes the steps ofproviding a molten metal including at least a first reactive metal in areactor, injecting steam into the molten metal to react a first portionof the steam with the reactive metal to form hydrogen gas and a metaloxide, injecting a carbonaceous material into the molten metal to reactthe carbonaceous material with a second portion of the steam and formcarbon monoxide, extracting a gas stream from the reactor includinghydrogen and carbon monoxide and reacting the gas stream in the presenceof a catalyst to form methane gas. The methane gas can then be burned toproduce electricity, such as in a combined cycle generator.

According to another embodiment of the present invention, a method forthe production of methanol is provided. The method includes the steps ofproviding a molten metal having at least a first reactive metal in areactor, injecting steam into the molten metal to react a first portionof the steam with the reactive metal to form hydrogen gas and a metaloxide, injecting a carbonaceous material into the molten metal to reactthe carbonaceous material with a second portion of the steam and formcarbon monoxide, extracting a gas stream from the reactor includinghydrogen and carbon monoxide, and reacting the gas stream in thepresence of a catalyst to form methanol.

According to another embodiment of the present invention, a method forthe production of ammonia is provided. The method includes contactingsteam with the reactive metal in a reactor to reduce at least a portionof the steam and form hydrogen gas, contacting air with the reactivemetal to combust oxygen contained in the air and form a nitrogen gasstream, and extracting a gas stream from the reactor comprising hydrogengas and nitrogen gas. The hydrogen gas and nitrogen gas can then bereacted in the presence of a catalyst to form ammonia.

According to another embodiment of the present invention, a method forthe formation of a gas stream including hydrogen and at least a secondgaseous component is provided. The method includes contacting steam witha reactive metal in a reactor to oxidize the reactive metal and formhydrogen gas. At least a second material is contacted with at least oneof the steam and the reactive metal in the reactor to form a secondgaseous component. A gas stream is then extracted from the reactor thatincludes hydrogen gas and the second gaseous component. The second,gaseous component can be, for example, a carbon compound or a nitrogencompound.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the thermodynamic equilibrium of hydrogen, carbondioxide and methane at various temperatures.

FIG. 2 illustrates a binary phase diagram for a tin-iron metal mixturethat is useful in accordance with the present invention.

FIG. 3 illustrates the production rate of hydrogen as a function of ironcontent in the reactor according to an embodiment of the presentinvention.

FIG. 4 illustrates the production rate of hydrogen as a function of ironcontent and reaction temperature according to an embodiment of thepresent invention.

FIG. 5 illustrates a reactor that is useful according to an embodimentof the present invention.

FIG. 6 illustrates a process flow for continuous hydrogen production.

FIG. 7 illustrates a process flow for continuous synthesis gasproduction according to an embodiment of the present invention.

FIG. 8 illustrates the use of the steam/coal ratio to control the H₂:COratio according to an embodiment of the present invention.

FIG. 9 illustrates a process flow for the production of a synthesis gasfor methanol production according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, steam is contacted with both areactive metal and a second material within a reactor to form a gascomposition that includes at least hydrogen and a second gaseouscomponent. In one embodiment, the second material is a carbonaceousmaterial and the second gaseous component is carbon monoxide. Oxygencontained in a first portion of the steam preferentially reacts with thereactive metal to oxidize the reactive metal to a metal oxide and reducethe first portion of the steam to form a hydrogen-containing gas. Asecond portion of the steam reacts with the carbonaceous material toform carbon monoxide and hydrogen. In one embodiment, production of thesynthesis gas continues until the concentration of the reactive metal inthe reactor is reduced to a minimum concentration that is dictated byeconomics, at which point the injection of the steam is terminated.Then, a reductant is introduced into the reactor to reduce the metaloxide back to the reactive metal. By switching between a flow of steamand carbonaceous material and a flow of reductant between two or morereactors, synthesis gas can be produced substantially continuously.

According to the present invention, syngas can be produced and extractedfrom the reactor having a controlled ratio of hydrogen to carbonmonoxide. Advantageously, the syngas can have a higher ratio of hydrogento carbon monoxide than synthesis gas produced in the prior art,particularly by the gasification of coal, and does not require theremoval of carbon oxides from the synthesis gas to produce a syngas withthe appropriate H₂ to CO ratio prior to forming high-value hydrocarbonssuch as methane and methanol. In addition, the synthesis gas can have arelatively low concentration of carbon dioxide.

According to the present invention, at least a portion of the steam iscontacted with a reactive metal, preferably a molten metal, disposed ina reactor. The reactive metal is reactive with steam to form hydrogengas and a metal oxide in accordance with Equation 9.xMe+yH₂O→yH₂+Me_(x)Oy   (9)

The reactive metal preferably has an oxygen affinity that is similar tothe oxygen affinity of hydrogen and reacts with the steam to form themetal oxide. For example, the reactive metal can be selected from thefollowing metals or their alloys: germanium (Ge), iron (Fe), zinc (Zn),tungsten (W), molybdenum (Mo), indium (In), tin (Sn), cobalt (Co) andantimony (Sb). A particularly preferred reactive metal according to thepresent invention is iron and according to one embodiment the reactivemetal is molten iron.

According to one preferred embodiment, the reactive metal is at leastpartially dissolved within a second metal or mixture of metals. Themetal into which the reactive metal is dissolved is referred to hereinas the diluent metal. The diluent metal may also be reactive with steam,in which case it can be selected from the group of reactive metalsdisclosed hereinabove, provided that the diluent metal is less reactivethan the reactive metal. Alternatively, the diluent metal may beselected from the metals wherein the oxygen partial pressure (pO₂) inequilibrium with the metal and oxides together is relatively high. Theseinclude nickel (Ni), copper (Cu), ruthenium (Ru), rhodium (Rh),palladium (Pd), silver (Ag), cadmium (Cd), rhenium (Re), osmium (Os),iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), lead (Pb), bismuth(Bi), selenium (Se) and tellurium (Te). More than one diluent metal canbe utilized in the molten metal mixture. The diluent metal should not bea metal wherein the oxygen partial pressure in equilibrium with metaland metal oxide together is extremely low.

Preferably, the diluent metal should: (1) combine with the reactivemetal to be liquid in the temperature range of about 400° C. to 1600°C.; (2) have a very low vapor pressure over this temperature range; and(3) have the capacity to hold the reactive metal in solution. Accordingto a preferred embodiment of the present invention, the diluent metal istin and in one embodiment, the diluent metal consists essentially oftin. However, the molten metal mixture can also include additionaldiluent metals, particularly copper and nickel.

A particularly preferred molten metal mixture for steam reduction toform hydrogen according to the present invention includes iron as thereactive metal and tin as the diluent metal. Iron has a high solubilityin molten tin at elevated temperatures and the melting temperature ofthe mixture is substantially lower than the melting temperature of pureiron (1538° C.). Although tin is also reactive with steam, it is lessreactive than iron. The tin-iron system is disclosed in detail inco-pending U.S. patent application Ser. No. 10/085,436 entitled “Methodfor the Production of Hydrogen and Applications Thereof” which isincorporated herein by reference in its entirety.

Due to thermodynamics, steam reduction reactions to form hydrogen gasfrom a metal require an excess of steam well above the stoichiometricrequirement. This excess of steam according to the present inventionenables the formation of hydrogen gas and thereby increases the ratio ofhydrogen to carbon monoxide in the synthesis gas extracted from thereactor.

The total steam requirement for hydrogen production (the mass ratio ofsteam required to hydrogen produced) using iron is much less than fortin at all temperatures. Additionally, iron will preferentially oxidizein the molten metal mixture. While not wishing to be bound by anytheory, it is believed that some reactive tin is oxidized to tin oxide,but is immediately reduced back to tin: $\begin{matrix}{\quad{{{2H_{2}O} + {Sn}}->{{SnO}_{2} + {2H_{2}}}}} & (10) \\{\quad\underset{\_}{{{SnO}_{2} + {2{Fe}}}->{{2{FeO}} + {Sn}}}} & (11) \\{{{{Net}\text{:}\quad 2H_{2}O} + {Fe}}->{{FeO} + {2H_{2}}}} & (12)\end{matrix}$

The thermodynamic steam requirement for tin at 660° C. is approximatelyequal to the thermodynamic steam requirement for iron at 1200° C.However, the production of hydrogen using tin as a reactive metal at660° C. is not practical since the kinetics (i.e., the reaction rate)are very poor and therefore very long residence times (i.e., the timethat the steam is in contact with the tin) are required.

At 1200° C., the kinetics for both tin and iron are excellent. The steamrequirement for tin, however, is much greater than for iron. Theresidence time that the steam is in contact with the reactive metal isincreased by the use of a diluent metal. For purposes of illustration, acomparison of the thermodynamic steam requirement and the nominalresidence times at a temperature of 1200° C. and various pressures fordissolved iron (50 wt. % iron in tin) compared to pure tin isillustrated in Tables 3 and 4. Table 3 illustrates the total steamrequired to produce one ton of hydrogen at 1200° C. TABLE 3 SteamRequirement for Hydrogen Production Stoichiometric Thermodynamic SteamSteam Total Steam System pH₂/pH₂O (tons) (tons) (tons) Pure Tin 0.1188.94 76.01 84.94 Tin/Iron 1.732 8.94 12.21 21.15 (50:50 by weight)

Table 4 illustrates the nominal residence times of the steam at aproduction rate of 4.439 tons of hydrogen per hour. TABLE 4 NominalSteam Residence Time Nominal Total Steam Melt Residence Time (seconds)System (m³/hr) Volume (m³) 1 atm. 5 atm. 10 atm. Pure Tin  2.51 × 10⁶17.93 0.026 0.13 0.26 Tin/Iron 0.625 × 10⁶ 24.41 0.141 0.70 1.41 (50:50by weight)

It is evident from the data in Tables 3 and 4 that pure tin systemsrequire substantially more steam to produce hydrogen than the dissolvediron systems in accordance with the present invention. Table 4 alsoshows that the nominal residence time available for tin to react withthe steam is considerably less than the nominal residence time availablefor iron dissolved in tin to react with the steam. Nominal or apparentresidence time is the time available for the steam (reactant of theprocess) to traverse the space occupied by the quantity of reactivemetal employed. In Table 4, the melt volume is the quantity of metalrequired by stoichiometry at the hydrogen production rate of 4.439 tonsof hydrogen per hour. During this time, ideally, hydrogen will beproduced in an amount corresponding to the thermodynamic pH₂/pH₂O ratio.An amount of reactive metal greater than the stoichiometric amount maybe used to increase nominal residence time, but the consequence isincreased reactor size and cost. Increased pressure also increases thereaction time available between the steam and the reactive metal,however, this also adds to cost.

Thus, one advantage of utilizing a reactive metal dissolved in a diluentmetal in accordance with the present invention is that the residencetime of the steam within the reactor is increased with respect to themass of the reactive metal. That is, a given mass of iron will occupy afirst volume as pure iron, but the same mass of iron will be distributedover about twice the volume if the iron is in a 50 weight percentmixture with a diluent metal such as tin.

FIG. 2 illustrates a phase diagram for iron and tin adapted from HariKumar, K. C., et al., Calphad, 20, 2, 139-149 (1996). It can be seenfrom FIG. 2 that one effect of adding iron (the reactive metal) to tin(the diluent metal) is to substantially lower the melting temperature ofthe iron. The liquidus of the metal mixture decreases from 1538° C.(pure iron) to about 1134° C. at a melt composition of about 48.7 weightpercent tin and 51.3 weight percent iron.

According to one embodiment of the present invention, it is preferredthat the metal mixture be maintained at a temperature above the liquidusline AC of FIG. 2 (e.g., above 1134° C.). A metal-steam reactiontemperature that is too high, however, adds significantly to theoperating costs. For the completely molten iron/tin system illustratedin FIG. 2, the melt should be maintained at a temperature above theliquidus temperature of about 1134° C., more preferably at a temperatureof at least about 1200° C. For the purpose of reasonable economics, thetemperature should not be greater than about 1500° C. and morepreferably is not greater than about 1400° C. A particularly preferredtemperature range for the completely molten tin/iron metal mixture isfrom about 1200° C. to 1300° C. At 1200° C., about 50 weight percentiron dissolves in tin with sufficient superheat and the mixture stays inthe molten state as iron is oxidized. Also, the reaction between steamand liquid iron dissolved in tin to form pure hydrogen at 1200° C. isalso quite vigorous and the reaction kinetics are excellent.Furthermore, the thermodynamics for the steam/iron system at 1200° C.are relatively good, requiring an excess of only about 12.2 tons ofsteam to produce each ton of hydrogen (1.37 moles of steam per mole ofhydrogen).

According to this embodiment, it is preferred that that the metalmixture initially include at least about 3 weight percent iron in themolten metal mixture, more preferably at least about 10 weight percentiron, even more preferably at least about 20 weight percent iron andmost preferably at least about 50 weight percent iron in the moltenmetal mixture. Further, the amount of iron in the molten metal mixtureshould preferably not exceed about 85 weight percent and more preferablyshould not exceed about 80 weight percent. The balance of the metalmixture in a preferred embodiment consists essentially of tin.Accordingly, the amount of tin in the system is preferably not greaterthan about 97 weight percent, more preferably is not greater than about90 weight percent and even more preferably is not greater than about 80weight percent. The molten metal mixture preferably includes at leastabout 15 weight percent tin and more preferably at least about 20 weightpercent tin.

According to another embodiment, insoluble phases such as in the form ofparticles can be dispersed within the molten metal. This assembly of amolten metal and an insoluble phase is termed a slurry. According to oneembodiment, a portion of the steam is contacted with a slurry thatincludes a molten metal mixture and a solid second phase, wherein thesolid second phase includes reactive metal-containing particles and isadapted to supply additional reactive metal to the molten metal mixture.Preferably, the particles are metallic particles (e.g., not oxideparticles). For example, the slurry could include iron-rich metallicparticles within an iron/tin melt that is saturated with iron. As thesteam reduction process proceeds, dissolved iron is removed from themolten metal mixture by oxidation of the iron and additional iron fromthe iron-rich particles dissolves in the molten metal to keep the moltenmetal portion of the slurry saturated with iron.

Referring again to the phase diagram in FIG. 2, the composition withinthe two-phase region defined by point A (83.3 wt. % Fe at 1134° C.),point B (84 wt. %. Fe at 1134° C.), point C (12 wt. % Fe at 895° C.) andpoint D (3 wt. % Fe at 895° C.) includes an iron/tin melt with about 3wt. % to 84 wt. % total iron, with a portion of the iron as iron-richmetallic particles dispersed in the melt. At a given temperature betweenabout 895° C. and about 1134° C., as iron is removed from the moltenmetal due to iron oxidation, additional solid iron from iron-richparticles will dissolve, thereby maintaining the level of iron in themelt at bulk saturation until the solid iron is depleted. Thisreplacement of iron that is lost to oxidation by iron originating fromthe iron-rich particles keeps the activity of the iron high, which, inturn, maximizes the production of hydrogen. For example, at atemperature of about 950° C. and about 50 wt. % total iron, the moltenmetal mixture will include about 4 wt. % dissolved iron in the system.As the dissolved iron is oxidized, additional iron metal from theiron-rich particles will dissolve to maintain 4 wt. % dissolved iron inthe melt. The activity of the iron, therefore, remains unchanged as aconsequence of dissolution of iron-rich particles.

Thus, according to this embodiment, the slurry, comprised of the moltenmetal mixture and iron-containing particles, is maintained at atemperature below the liquidus temperature of 1134° C. and is at leastabout 895° C., more preferably from about 900° C. to about 1134° C.

One advantage of such a method is that the activity of the iron remainsconstant and in fact is close to one, and therefore the production rateof hydrogen due to the reduction of steam remains constant and maximizedthroughout the process. The desired effect of constant activity of thereactive metal would also be observed if the process were carried outwithin the miscibility gap region of FIG. 2; however, the activity ofiron would be somewhat less than one.

A thermodynamic relationship exists between the partial pressure ofhydrogen in the off-gas, the reaction temperature and the weight percentiron in the molten metal composition. The thermodynamic quantity,referred to as the “activity” of iron, varies as a function of ironconcentration and strongly influences the ratio of hydrogen to water inthe off-gas. The production of hydrogen is maximized by operating withinphase regions that establish a high iron activity over a widecomposition range through the use of a second phase in equilibrium withthe reacting phase. This applies both to the liquid-liquid region, abovethe line AC in FIG. 2, as well as the solid-liquid region, below theline AC and to the right of the line AB. However, the present inventiondoes not exclude operation in the iron-rich liquid phase.

FIG. 3 illustrates the relationship between the level of hydrogen in theoff-gas as a function of iron content in the molten metal mixture andignoring the reaction of the carbonaceous material. FIG. 3 wascalculated based on thermodynamics of the steam/metal reaction at 1225°C. It is evident that the hydrogen production rate rapidly decreases asthe iron content drops from 20 weight percent to 10 weight percent. FIG.4 illustrates the hydrogen production as a function of temperature andiron content, again ignoring hydrogen production due to reaction of thecarbonaceous material.

At levels below about 20 weight percent iron and temperatures aboveabout 1134° C., the production capacity for hydrogen is impaired since:(1) the pH₂/pH₂O drops significantly; and (2) only short periods of timeare available before gas flows (i.e., steam and metal oxide reductant)have to be switched.

The reactor temperature can be controlled to maintain a substantiallyconstant temperature by controlling the incoming steam temperature andquantity and/or by adding oxygen to the reactor, as is discussed in moredetail below.

The reactor can be maintained at an elevated pressure if necessary foradequate steam residence time in the reactor. For example, it may bedesirable to maintain an elevated pressure, such as about 2 atmospheres(about 29 psi). Syngas typically requires several stages of compressionto secure the high pressures required for either transmission bypipeline or as a first step in the subsequent synthesis of hydrocarbons(a methane synthesis loop for example). Operating the reactor atslightly elevated pressure (2 atmospheres, for example) significantlyreduces the capital and energy cost associated with the first stage ofcompression. The high cost of the first stage of compression is relatedto the low density of the hydrogen-rich syngas. However, significantlyincreased pressure in the reactor adds to capital cost and therefore thepressure in the hydrogasification reactor is preferably not greater thanabout 3 atmospheres (about 44 psi).

According to the present invention, a slag layer is maintained over themolten metal mixture. A slag layer provides a number of advantages,including preventing the metal oxide, e.g., iron oxide, from exiting thereactor. The temperature in the hydrogasification reactor should besufficient to maintain the slag layer that forms over the metal mixturein the molten state over a range of compositions. For a mixed metalsystem, as the reactive metal is oxidized a decrease will occur in theconcentration of the reactive metal in the metal mixture and the metalmixture should remain molten as the reactive metal is oxidized. Similarto the range of compositions for the molten metal discussed previouslywith respect to FIG. 2, the range of slag compositions required toensure adequate slag fluidity and reactivity, and prevent foaming can beadjusted, as necessary, for a given temperature. For example, fluxes canbe added to the reactor to adjust the properties of the slag. One fluxsystem is indicated by the liquid surface of SiO₂, FeO, CaO, MgO, Na₂Oand K₂O. However, sulfur and other cations may be incorporated in thisor other slags to secure satisfactory slag chemistry.

The metal oxide (e.g., w

stite and/or magnetite) that is generated by steam reduction canadvantageously be trapped (dissolved or suspended) in a slag layerwithin the reactor. At the preferred temperatures, the metal oxide isincorporated into the slag, which is lighter than the metal mixture.Therefore, as the dissolved metal is depleted from the molten metalmixture, the metal oxide rises through the molten metal and contributesto the slag layer on top of the molten metal. It is an advantage of thisembodiment of the present invention that the oxide formed upon reactionof the reactive metal with the steam has a density that is less than thedensity of the molten metal, whereby the metal oxide rises to the slaglayer. Preferably, the metal oxide is at least about 10 percent lessdense than the molten metal. This also enables the metal to sink fromthe slag layer to the molten metal mixture upon reduction of the metaloxide. This accumulation of iron oxide in the slag may require theaddition of a flux such as SiO₂, FeO, CaO, MgO, Na₂O, K₂O or mixturesthereof to maintain the slag in the preferred condition with respect toviscosity, reactivity, foaming, and the like.

Accordingly, a portion of the steam introduced to the hydrogasificationreactor is reduced by reaction with the reactive metal to form a metaloxide. In addition to the steam, a carbonaceous material is alsoinjected into the molten metal and a second portion of the steam reactswith the carbonaceous material to form carbon monoxide and hydrogen. Thecarbonaceous material can include crude oil, tar sand or a similarsubstance, pet coke, municipal waste, hazardous waste, biomass, tiresand/or any combination thereof. In a preferred embodiment, thecarbonaceous material includes coal and the following description refersto coal as the carbonaceous material, although it will be understoodthat the present invention is not limited thereto. The coal can be alow-grade coal as well as a high-grade coal. The coal can optionally bepre-treated such as by comminuting the coal to reduce the particle sizeof the coal, although the particle size of the coal or othercarbonaceous material is not critical to the practice of the presentinvention.

The reactants (e.g., steam, coal and molten metal) must be containedwithin a suitable reactor and maintained under suitable reactionconditions. Further, the reactants should be provided in a mannerconducive to good mixing and high contact surface area. High-temperaturereactors suitable for establishing good gas/liquid contact are utilizedin the chemical, and especially metallurgical industries.

For example, bath smelting reactors can be used for carrying out themethod of the present invention. Bath smelters have been used for theefficient reduction of iron oxides (e.g., fine iron ore and iron-richsecondary materials) using carbonaceous materials, including those otherthan metallurgical coke, for reduction. The reactants are typicallyinjected into a molten metal bath using a water-cooled lance. Examplesinclude the Hismelt technology, such as described in U.S. Pat. No.3,751,019 by Phillips and the Ausmelt technology, such as described inU.S. Pat. No. 5,282,881 by Baldock et al. Each of these U.S. patents isincorporated herein by reference in its entirety. These systemsadvantageously utilize a stationary lance, enabling the reactor to besealed for operations at elevated pressures, if necessary.

One reactor system that is useful according to the present inventionutilizes a top-submerged lance (TSL) to inject the steam into the moltenmetal below the surface of the molten metal. Such reactors have beenused for the commercial production of tin from tin ore (cassiterite).Examples of reactors utilizing a top-submerged lance to inject reactantsare disclosed in U.S. Pat. No. 3,905,807 by Floyd, U.S. Pat. No.4,251,271 by Floyd, U.S. Pat. No. 5,251,879 by Floyd, U.S. Pat. No.5,308,043 by Floyd et al. and U.S. Pat. No. 6,066,771 by Floyd et al.Each of these U.S. patents is incorporated herein by reference in theirentirety. Such reactors are capable of injecting reactants (e.g., steam)into the molten metal at extremely high velocities, approaching Mach 1,thereby promoting good mixing of the reactants. Although the followingdescription refers to the use of a reactor including a top-submergedlance, it will be appreciated that other types of reactors can beutilized in accordance with the present invention.

The major function of the top submerged lance (TSL) furnace is tomaximize contact between the solids, liquids and gases. FIG. 5 is aschematic illustration of such a reactor. The reactor 500 includesrefractory sidewalls 502 that are adapted to contain the molten metal504. A side-penetrating lance 518 penetrates the furnace near the bottomof the reactor and is provided for the optional introduction of oxygenfor the purpose of heating the reactor 500. A top-submerged lance 508 isdisposed through the reactor top wall 512 and is adapted to inject coalentrained by steam into the metal 504 at a high velocity. Preferably,the top-submerged lance 508 terminates and injects steam and coal belowthe surface of the slag layer 506 and near the interface of the moltenmetal 504 and the slag layer 506.

The temperature of the steam-entrained, particulate coal increasesrapidly from ambient temperature to the reactor temperature. Caking ofthe coal particles is not a significant issue since the particles havevirtually no opportunity to coalesce before passing the temperatureregion where caking can occur. Rapid devolatilization of the coalparticles occurs as the particles approach the reactor temperature.

When the coal and steam come in contact with the molten metal 504, aseries of physical and chemical reactions occur. According to thepresent invention, a portion of the steam reacts with the reactive metalproducing hydrogen and a metal oxide, and the metal oxide rises and isincorporated into the slag, as is discussed above.

At temperatures above 800° C., the coal partitions into volatile matterand coke or char comprised of the fixed carbon and ash. The volatilematter reacts with the steam to form hydrogen and carbon monoxide. Theseproducts are the sum of the reactions given in Equations 1, 5 and 7,although Equation 7 proceeds in the opposite direction shown and isknown as the steam methane reformation reaction. The volatilesdisproportionate into methane and carbon and both of these species reactwith steam to produce hydrogen and carbon monoxide, respectively.

The steam also reacts with carbon contained in the coke (or char) toform hydrogen and carbon monoxide. This highly endothermic reaction(Equation 5) requires heat, which can be provided in at least four ways,which are described in detail below.

The formation of hydrogen by reduction of a portion of the steam withthe reactive metal enables control of the H₂:CO ratio in the synthesisgas that is extracted from the reactor. That is, a variable amount ofhydrogen is produced by the steam/reactive metal reaction, variable inproportion to the quantity of steam used and a mixture of hydrogen andcarbon monoxide are formed in a fixed proportion by thesteam/hydrocarbon reaction, which is dependant upon the reactortemperature, the quantity of coal and steam (and oxygen, if any)employed and the type of coal. Thus, sufficient steam is provided toreact with both the coal and with the reactive metal. The foregoingreactions proceed until the reactive metal is oxidized to a lower limit,established by economics. At this point the introduction of steam isstopped and, after purging, a reductant (e.g., coal and air) isintroduced into the reactor for the purpose of reducing the metal oxideback to the metal.

The regeneration of the reactive metal from the metal oxide can occur ina number of ways. In one preferred embodiment, carbon from thedevolatilization of coal is used as a reductant (volatile matter fromthis devolatilization may be directed to the gasification reactor.). Thecarbon entering the metal oxide regeneration reactor is contacted withthe metal oxide dissolved in the slag layer and reacts to form thereactive metal and carbon monoxide. The metal gravitates to the moltenmetal bath where it replaces the reactive metal first reacted withsteam. The carbon monoxide rises through the molten metal and fluid slaginto the freeboard (open space) above the charge. Air is introduced intothis space and the carbon monoxide is oxidized by the air to carbondioxide, releasing significant quantities of heat. Also, if thevolatiles released by the devolatilization of the coal are not directedto the gasification reactor, they can be combusted, releasing additionalheat. This heat is required to maintain the carbon/metal-oxide reactionand compensate for furnace heat losses.

For the coal hydrogasification reactions to proceed continuously, a heatbalance must be achieved around the gasification reactor. That is, heatbrought into the reactor by the feed materials plus heat generated bychemical reactions within the reactor must equal heat leaving with theproducts plus heat leaving as environmental losses. For coalhydrogasification, heat must be supplied. Admitting oxygen into thereactor is one method for producing heat, and the amount of heatproduced is proportional to the amount of oxygen introduced, whichpermits control over the reactor temperature.

At least two techniques for introducing oxygen into the furnace arepossible according to the present invention. The oxygen can beintroduced down the top-submerged lance 508 with the steam and coal, orcan be introduced independently at some other location, such as byside-penetrating lance 518.

However, the use of oxygen to generate heat in the reactor consumes asubstantial quantity of the reactive metal, leaving less iron availablefor generating hydrogen. The reduction in hydrogen availability meansthat less coal can be admitted to the reactor if the specified H₂:CO isto be maintained. Accordingly, less synthesis gas is produced and thecost of utilizing oxygen for heat is about twice the cost ofsuperheating the melt.

The melt (slag and molten-metal mixture) can be superheated during theregeneration of the reactive metal. Thus, reactor 500 can contain asuperheated melt at the start of its cycle. As the chemical reactionsproceed in reactor 500, and because insufficient heat is available tomaintain the temperature, the temperature begins to fall. As thetemperature decreases, some of the sensible heat of the melt is releasedsupplying the heat needed in reactor 500. The amount of sensible heatreleased is a product of the specific heats of the molten metal and slagmultiplied by their masses and multiplied by the temperature decrease.

Controlling either or both the mass of melt that is superheated and thetemperature of the superheat can control the amount of sensible heatgained and then released. To preserve the life of the refractory brickslining of reactor 500, it is desirable to minimize the temperatureswing. The mass of melt, correspondingly, must be increased to maintainthe same sensible heat gain/loss. For example, assume that reactor 500is six meters in diameter and a superheat of 237° C. is needed to impartthe sensible heat required for heat balance. A preferred method tosupply the same amount of sensible heat but with far less thermal shockto the refractory bricks is to increase the diameter of reactor 500 toeight meters (i.e., oversize the reactor in relation to the otherprocess equipment) and provide a superheat of only 100° C. This ispossible because the mass of melt in an eight-meter diameter reactor is2.37 times the mass of melt in a six-meter diameter reactor, assuminggeometric similitude between reactors.

The larger mass of metal and slag in the oversized (e.g., eight-meterdiameter) reactor affords several advantages in addition to assisting inthe heat balance about the reactor. The larger mass of melt and slagmeans that the variation of the percent reactive metal oxide in the slagand reactive metal in the melt can vary between narrower limits than forthe smaller mass of slag and melt. These narrower limits areadvantageous because the thermodynamic activity of the reactive metaland reactive metal oxide remain closer to unity, which facilitates thereactions. Alternatively, the larger mass of melt and slag can permitlonger cycle times. Also, the larger mass of melt will permit increasedproduction of hydrogen, syngas or ammonia, thereby shortening cycletimes and effectively lowering capital cost.

The hydrogasification process is continued until the quality of thesynthesis gas decreases to a sufficiently low level. Typically, thiswill result from a depletion of the reactive metal and a resultingdecrease in the hydrogen content of the synthesis gas. At this point,the injection of steam is terminated and a reductant is introduced intothe reactor containing the molten metal and the slag to reduce the metaloxide back to the metal

In this regeneration step, which can be viewed as reductive cleaning ofthe slag, the metal oxide in the slag is reduced and returned to themelt as the reactive metal. This is achieved by lowering the oxidationpotential of the system through introduction of reductant to thereactor. The reductant can be carbon monoxide, which is preferable whenoperating at temperatures below 1000° C., or carbon derived from coal,petroleum coke, waste, other carbon source, which is preferable above1000° C. According to a preferred embodiment, operating at a temperatureabove 1000° C., the oxidation potential of the system is lowered byinjecting particulate carbon, hydrocarbon or liquid hydrocarbon into themelt under conditions of intense mixing. The particulate carbon orhydrocarbon is preferably coke, but may include coal or other organicmaterial. A liquid hydrocarbon, such as #6 or other oil can also beused. Waste materials such as scrap tires, biomass, animal waste, ormunicipal waste may also be used.

Prior to injection of a reductant, the reactor may be purged, such aswith steam, to remove any gases from the reactor. After the reductivecleaning of the slag is complete, the reactor may again be purged, withair or steam, for the purpose of removing any carbon that may bedissolved in the metal and/or for the purpose of removing any othertramp elements that may be in either the melt or slag and that otherwisewould contaminate the synthesis gas.

FIG. 6 illustrates a process for continuous generation of hydrogen usingtwo reactors as disclosed in the co-pending U.S. patent application Ser.No. 10/085,436 entitled “Method for the Production of Hydrogen andApplications Thereof,” and incorporated herein by reference in itsentirety.

The hydrogen generation process employs two reactors 602 and 604 whereinone of the reactors operates in steam reduction mode while the otheroperates in metal oxide reduction mode. As illustrated in FIG. 6, thereactor 602 is operating in steam reduction mode and generates hydrogen,and reactor 604 is operating in metal oxide reduction mode, wherein thereactive metal is iron.

Steam is provided by heating water in waste heat boilers 606 and 610.Prior to heating in the boilers, the water should be subjected topurification 612 such as by using reverse osmosis and de-ionization toremove contaminants that can affect boiler operation or introduceimpurities into the hydrogen product gas. Steam is produced in theboilers and is provided to the reactor 602 at a super-heated temperaturethat is sufficient to maintain isothermal conditions within the steamreduction reactor 602 at the operating temperature, e.g., about 1200° C.

The steam is injected into the reactor 602 through a top-submerged lance608. The top-submerged lance provides good mixing and a high contactsurface area between the steam and the molten metal mixture to promotethe steam reduction/metal oxidation reaction. The reactor 602 is sealedto prevent egress of hydrogen and steam from the reactor. Also, thereactor may be placed under modest pressure to provide a sufficientcontact time for the steam and to deliver the hydrogen under pressure.

Other materials can be added to the reactor if necessary. For example,fluxes 614 can be added to control the properties of the slag layer thatforms above the molten metal mixture as the steam reduction reactionoxidizes the metal. Possible fluxes include SiO₂, FeO, CaO, MgO, Na₂O orK₂O. Additionally, other materials such as tin compounds, cassiteriteore or other materials such as iron compounds or ore may be added tomake-up for losses of metal values. According to a particularlypreferred embodiment, cassiterite ore (SnO₂) is injected into thereactor to make-up for tin losses.

A hydrogen-containing gas that includes hydrogen and excess steam isremoved from the reactor 602. The hydrogen-containing gas can be passedthrough the waste heat boiler 606 to provide heat for additional steam,thereby conserving heat values. The hydrogen-containing gas stream canalso include some contaminants, such as the sub-oxide of tin oxide(SnO), the hydrated sub-oxide of tin (SnO₂H₂), and entrainedparticulates of (frozen) slag which are ejected from the molten metalbath and slag, and such contaminants can be removed in a baghouse 616.For example, the volatile tin compounds can be condensed from the gasstream and along with particulate slag can be captured either in thewaste heat boiler or in the baghouse. After being captured, thesematerials can be pelletized 618 and optionally provided to eitherreactor 602 operating in steam reduction mode or reactor 604 operatingin the metal oxide reduction mode for recovery of metal values andcontrol of the slag chemistry. After removal of contaminants, if any,the hydrogen gas stream is treated in a condenser 620 and/or chiller tocondense the excess steam from the hydrogen gas stream and form a highpurity hydrogen gas stream 622. Water condensed from the hydrogen gasstream can be recycled for additional steam production.

Simultaneously, metal oxides are reduced in reactor 604. The metaloxides are reduced by a reductant as is described above, such as carbonor carbon monoxide according to the following chemical equations:Me_(x)O_(y)+yC→yCO+Me_(x)   (13)Me_(x)O_(y)+yCO→yCO₂+Me_(x)   (14)

Carbon may be derived from virtually any carbonaceous material such ascoal, petroleum coke, biomass and organic waste materials, includingmunicipal waste and hazardous waste. It is possible to add thecarbonaceous material into the reactor 604 by simply dropping it in thereactor. Carbon monoxide can be formed by injecting coal 624 or othercarbonaceous material and oxygen 626 through a top-submerged lance 628.As with reactor 602, the top-submerged lance 628 provides good mixingand contact surface area between the reactants. The oxygen-containinggas is also preferably injected using a top-submerged lance or similardevice.

Air is admitted above the metal/slag charge for the purpose ofcombusting any carbon monoxide that may be present. This combustionreflects heat back down into the melt where it is needed for the metaloxide reduction reaction. Further, the presence of a small excess of air(typically 3 percent) precludes discharge of carbon monoxide into theatmosphere.

The ash-forming minerals that are typically part of the coal (or othercarbonaceous material) used as a reductant contribute to the slag layerwithin the reactor 604. When coal (or other carbonaceous material) isused as feedstock 624 and there is adequate calcium oxide (CaO) in theslag, the slag layer can be a salable pozzolanic by-product. As withreactor 602, other materials such as fluxes can be injected into thereactor 604, for example to control the properties of the slag such asslag fluidity or tendency to foam. The off-gas from the metal oxidereduction reactor 604 can include carbon dioxide, nitrogen and somecontaminants from the coal such as sulfur. Heat from the off-gas can beconserved in the waste heat boiler 610 where steam is generated. The gasstream can then be treated in a bag-house 630 to remove particulatecontaminants. The remaining gases can be treated in a limestone scrubber632 to form environmentally benign stack gases and gypsum from thesulfur that originates from the coal. Alternatively, the sulfur can bescrubbed with aqueous ammonia to form ammonium sulfate, a usefulcompound for fertilizing soil.

Thus, as iron is depleted from the molten metal mixture in the steamreduction reactor 602, and as the iron oxide is reduced to metal in themetal oxide reduction reactor 604, their functions can be reversed byswitching the flows into the reactors and the flows of the cooled gasesafter the waste heat boilers. Prior to switching gas flows, the reactorscan be purged to remove residual gases and contaminates, if any.Accordingly, hydrogen gas can be produced in a substantially continuousmanner.

FIG. 7 illustrates a process flow for continuous synthesis gasproduction according to an embodiment of the present invention toproduce a tailored H₂:CO ratio syngas. Hydrogen, added by the steam-ironreaction, supplements the hydrogen produced by gasification to increasethe overall H₂:CO ratio.

A tailored synthesis gas can be produced if both a carbonaceous materialand steam are fed into the reactor that normally receives only steam forthe purpose of making hydrogen, i.e., reactor 602 in FIG. 6. Forhydrogen production, only the reactor operating in metal oxide reductionmode receives carbonaceous material, while for gasification according tothe present invention, both reactors receive carbonaceous material.

Referring again to FIG. 7, the synthesis gas generation process employstwo reactors 702 and 704 wherein one of the reactors operates in steamreduction and gasification mode while the other operates in metal oxidereduction mode. As illustrated in FIG. 7, reactor 702 is operating insteam reduction mode and generates tailored synthesis gas 722 andreactor 704 is operating in metal oxide reduction mode.

Steam is provided by heating water in waste heat boilers 706 and 710.Prior to heating in the boilers, the water should be subjected topurification 712 such as by using reverse osmosis and de-ionization toremove contaminants that can affect boiler operation or introduceimpurities into the synthesis product gas. Steam is produced in theboilers and is provided to the reactor 702 at a super-heated temperaturethat is sufficient to support a heat balance about reactor 702.

A carbonaceous material 738 is provided to the reactor 702. If thecarbonaceous material is a high Btu carbonaceous material, such ascomminuted scrap tires or high-rank coal, it is fed into the reactor 702through the submerged lance 708. However, if the carbonaceous materialis a low to medium Btu feedstock, such as municipal waste, animal waste,sewage sludge, low-rank coals, biomass or other medium to low Btuorganic materials it must first be dried in a dryer 736.

Steam is injected into the reactor 702 through a top-submerged lance708. The top-submerged lance 708 provides good mixing and a high contactsurface area between the steam, carbonaceous material and the moltenmetal to promote the steam reduction/metal oxidation reaction and thesteam-carbon reaction. The reactor 702 is sealed to prevent egress ofhydrogen, carbon monoxide and steam from the reactor (see FIG. 5). Also,the reactor may be placed under modest pressure to provide a sufficientcontact time for the steam and to deliver the synthesis gas underpressure.

Other materials can be added to the reactor 702 if necessary or desired.For example, fluxes 714 can be added to control the properties of theslag layer that forms above the molten metal mixture as the steamreduction reaction oxidizes the metal. Possible fluxes include SiO₂,FeO, CaO, MgO, Na₂O or K₂O. Additionally, other metal-containingmaterials such as tin compounds, cassiterite ore or other materials suchas iron compounds or ore may be added to make-up for losses of metalvalues. According to a particularly preferred embodiment, cassiteriteore (SnO₂) is injected into the reactor to make-up for tin losses whentin is used as a reactive metal or a diluent metal. A synthesis gas thatprincipally includes hydrogen, carbon monoxide, carbon dioxide andexcess steam is removed from the reactor 702. The synthesis gas can bepassed through a waste heat boiler 706 to provide heat for additionalsteam, thereby conserving heat values.

The synthesis gas stream can also include some contaminants, such as thesub-oxide of tin (SnO), the hydrated sub-oxide of tin (SnO₂H₂),entrained particulates of (frozen) slag and gaseous compounds that maybe formed from trace constituents associated with the carbonaceousmaterial. Such contaminants can be removed in a baghouse 716. Forexample, the volatile tin compounds can be condensed from the gas streamand, along with particulate slag, can be captured either in the wasteheat boiler 706 or in the baghouse 716. After being captured, thesematerials can be pelletized 718 and optionally provided to the reactor702 operating in steam reduction mode or, preferably, the reactor 704operating in metal oxide reduction mode for recovery of metal values andcontrol of the slag chemistry. Noxious gases derived from traceconstituents in the carbonaceous feedstock can be removed by scrubbing.

After removal of contaminants, if any, the synthesis gas stream istreated in a condenser 720 and/or chiller to condense the excess steamfrom the synthesis gas stream and form a high purity tailored syngasstream 722. Water condensed from the synthesis gas stream can berecycled for additional steam production. The tailored syngas can thenbe converted to methane or methanol in a catalytic conversion unit (notillustrated).

Simultaneously, metal oxides are reduced in the reactor 704. The metaloxides preferably are reduced by a reductant such as carbon, which canbe formed by injecting a carbon-containing feedstock 724 directly intothe reactor 704, such as through a top-submerged lance 728. As withreactor 702, the top-submerged lance 728 provides good mixing andcontact surface area between the reactants.

Carbon and heat are required to regenerate the iron in the reactor 704.Feedstocks containing a large percentage of carbon are preferable.Petroleum coke, particularly petroleum coke including over 80 percentcarbon is preferred. Char, the residue from coal or low-Btu organicfeedstocks, can also be used. The organic feedstock (coal or othercarbonaceous material) may be pyrolyzed in dryer/pyrolyzer 736, with thevolatiles from the pyrolysis directed to the reactor 702 to provide heatto reactor 702, resulting from their (volatiles) reaction with steam,and to offset some portion of the heat-consuming steam-carbon reaction.Dryer/pyrolyzer 736 may be for example a fluid bed combustor that usesoxygen and steam at about 1000° C. to supply the heat required to drythe coal and boil-off (expel) the volatiles.

That portion of the carbon in the carbonaceous material used to reducethe metal oxide is transformed into carbon monoxide. This carbonmonoxide is burned with air above the molten metal, reflecting heat backto the interior furnace walls and the molten metal. A portion of thecarbon feedstock can be burned to provide the requisite thermal energy.

Ash-forming minerals are typically part of the organic feedstock (orother carbonaceous material) that is employed along with oxygen to bringabout the reduction of the reactive metal oxides. Such ash-formingminerals contribute to the slag layer within the reactor 704.

As is discussed above with respect to reactor 702, other materials canbe injected into the reactor 704. For example, fluxes can be injected tocontrol the properties of the slag such as slag fluidity or tendency tofoam. The off-gas from the metal oxide reduction reactor 704 can includecarbon dioxide, nitrogen and some contaminants from the coke, such assulfur. Heat from the off-gas can be conserved in the waste heat boiler710 where steam is generated. The gas stream can then be treated in abag-house 730 to remove particulate contaminants. The remaining gasescan be treated in a limestone scrubber 732 to form environmentallybenign stack gases and gypsum (CaSO₄.2H₂O) from the sulfur thatoriginates from the coal. Alternatively, the sulfur can be scrubbed withaqueous ammonia to form ammonium sulfate ((NH₄)₂SO₄), a useful compoundfor fertilizing soil.

To conserve heat it may be desirable to keep the synthesis gas streamexiting the baghouse at its elevated temperature (400° C. to 500° C.)prior to being converted into methanol or methane. To do so, anhydrousammonia may be injected into the gas stream to react with the acid gascomponents producing ammonium sulfide ((NH₄)₂S), ammonium chloride(NH₄Cl) and ammonium fluoride (NH₄F). The ammonium salts that areproduced may be removed from the gas stream, for example by pulsedceramic filters. Thereafter, the purified gas stream can proceeddirectly to a conversion step without significant reheating.

Thus, as iron is depleted from the molten metal mixture in the steamreduction reactor 702, and as the iron oxide is reduced to metal in themetal oxide reduction reactor 704, their functions can be reversed byswitching the flows into the reactors and switching the gas flowsdownstream of the waste heat boilers. Prior to switching gas flows, thereactors can be purged to remove residual gases and contaminates, ifany. Accordingly, a syngas with a pre-chosen H₂:CO can be produced in asubstantially continuous manner.

A combination of factors is required to achieve a heat balance acrossboth of the reactors 702 and 704. First, reactor 704 incurs an increasein temperature of about 125° C. over the period of time that is requiredto reduce the iron oxide. Providing this increase only requires slightlyincreasing the fuel and air sent to reactor 704. This means that at thestart of its cycle, reactor 702 is superheated by about 125° C. Over theperiod of time that is required for the iron in reactor 702 to beoxidized by steam, the sensible heat of the charge in 702 is given upthereby supplying heat to support the hydrogasification chemistry.Second, the steam is preferably superheated to at least about 1000° C.to bring additional heat into reactor 702. Third, volatiles derived fromthe carbonaceous feedstock destined for reactor 704 are diverted intoreactor 702. This supplants some portion of the endothermic steam/carbonreaction for producing hydrogen and carbon monoxide with the exothermicsteam-volatiles reaction thereby lessening the heat requirement forreactor 702 and adding heat to that reactor. For heat balance reasons,organic feedstocks such as municipal waste, animal waste, sewage sludge,low-rank coals, biomass and other medium to low Btu organic materialsmust first be dried by dryer/pyrolyzer 736. Steam is available fromwaste process heat and can be used as a drying medium. Steam will alsocarry odors, frequently a problem in drying materials such as animalwaste, into the reactor 702 where organics are converted to simplenon-malodorous molecules (H₂, CO & CO₂) as part of the gasificationprocess. Various methods available for providing a heat balance aredescribed below.

In a preferred embodiment according to the present invention, areductant derived from the dryer/pyrolyzer 732 is injected into themolten metal and slag layer in the reactor 704. The feedstock can beinjected through the top-submerged lance with the air, or can be addedseparately. It is particularly advantageous to use coke pyrolized fromcoal as the reductant source, because it is both abundant and relativelyinexpensive compared to oil and gas. The use of scrap tires and otherwaste materials as feed for the reactor 704 can also supply some iron(e.g., from the steel belts). The metal oxide reduction process iscontinued until a sufficient amount of metal has been re-dissolved inthe molten metal.

Preferably, the reaction conditions when operating in the mode to reducethe metal oxide to metal are substantially identical to the conditionsduring hydrogasification. That is, it is preferred that the temperatureand pressure of the reactor 704 are the same or very similar to thetemperature and pressure of the reactor 702. Thus, the temperature ispreferably at least above the liquidus of the molten metal mixture(e.g., about 1134° C. for the tin/iron system) and in one embodiment isat least about 1200° C. Preferably, the temperature does not exceedabout 1600° C. and more preferably does not exceed about 1400° C. In aparticularly preferred embodiment, the temperature is about 1400° C. inreactor 702 and 1300° C. in reactor 704 at the start of their cycles,decreasing to 1300° C. in reactor 702 and increasing to 1400° C. inreactor 704 by the end of their cycles. The pressure should be slightlyabove atmospheric pressure in the reactor 702 and may be either slightlyabove or slightly below atmospheric pressure in the reactor 704. Apreferred option is to operate both reactors at from about 1 to 2atmospheres.

The steam-iron reaction in the reactor 702 produces hydrogen and amodest amount of heat. This heat of reaction is insufficient to offsetfurnace heat loss and provide a heat balance in the reactor 702.Therefore, as noted above, volatiles from the pyrolysis of organicfeedstock of reactor 704, are directed to reactor 702 to help maintainthe heat balance. Further, steam is admitted to reactor 702 at as high atemperature as is practicable, such as up to about 1000° C.

In the reactor 702 there are three reactions that produce hydrogen. Thefirst two are operative all the time and include the modestheat-producing steam-iron reaction (Equation 12) described above, andthe highly endothermic steam-carbon reaction (Equation 5). The third isthe exothermic steam-volatiles reaction.

The benefit of the third reaction relative to heat balance depends uponthe amount of volatiles being admitted into reactor 702. To maximize theamount of volatiles, feedstock to the reactor 704 is pyrolyzed and thereleased volatiles are directed into the reactor 702. Pyrolysis of thefeedstock disproportionates the feedstock into: (1) char, principallycomposed of carbon and ash, directed to the reactor 704 for reducing themetal oxide; and (2) volatile matter (volatiles) comprised predominantlyof carbon, hydrogen and oxygen, directed into the reactor 702. When thevolatile matter reaches the temperature in the reactor 702 and steam ispresent, it is immediately rendered into hydrogen and carbon monoxidewith the release of heat.

The steam-carbon reaction (Equation 5) is the principal gasificationreaction. To sustain this endothermic reaction, a significant amount ofheat must be furnished to the reactor 702. The required heat can besupplied to the reactor in at least four ways:

-   -   1. Oxygen can be added to the reactor 702 to react with carbon        and iron and form their respective oxides. Both reactions are        strongly exothermic.    -   2. The reactor 702 may be heated electrically by inductive        coupling with an external source of electricity. Electricity can        be generated from process steam raised by cooling the exit gases        from reactor 702. Other means of electrical heating are        possible, such as plasma torch heating.    -   3. The molten metal and slag in reactor 702 may be superheated        during the prior stage regeneration of the reactive metal from        the reactive metal oxide. Additional fuel (724 into reactor 704)        is required. The sensible heat of the superheated mass of molten        metal and slag that is available as the molten mass cools meets        the endothermic requirement of the steam-carbon reaction.    -   4. Some portion of the steam-carbon reaction may be supplanted        by supplying hydrogen and carbon monoxide derived from the        volatile matter of the feedstock to the reactor 704. The        reactions, which produce CO and H₂ from volatile matter, are not        highly endothermic like the steam-carbon reaction. The        requirement for CO and H₂ from the endothermic steam-carbon        reaction is effectively reduced, as is the required heat.

As discussed in detail above, the addition of oxygen can adverselyaffect the economics of synthesis gas generation. Heating the reactoradds additional costs to the process. The preferred method of addingheat to the reactor 702 is to superheat the molten metal and add thevolatile fraction of the feedstock of the reactor 704 to the reactor702.

In accordance with the foregoing, the synthesis gas includes at least H₂and CO. Other components can include H₂O, CO₂ and CH₄. It is generallypreferred that the gas stream extracted from the reactor include atleast about 50 vol. % H₂ and that the CO₂ content be not greater thanabout 15 vol. %, more preferably not greater than about 10 vol. %. Inaddition, the carbonaceous material, particularly coal, can includeimpurities that form acid gas components in the gas stream. Conventionalapproaches for removing the acid gas components such as hydrogen sulfide(H₂S), hydrogen chloride (HCl) and hydrogen fluoride (HF) may be used toclean the gas stream, if necessary. Alternatively, ammonia may beinjected into the hot (400° C. to 500° C.) gas stream to react with theacid gas components producing, respectively, ammonium sulfide ((NH₄)₂S),ammonium chloride (NH₄Cl) and ammonium fluoride (NH₄F). The ammoniumsalts that are produced may be removed from the gas stream, for exampleby pulsed ceramic filters. Thereafter, the purified gas stream canproceed directly to a conversion step, such as methanation, as isdiscussed below. If a slight excess of ammonia is left in the gas streamand the gas stream is converted to methane, the ammonia will burn whenthe methane is burned yielding water and nitrogen. The net heat ofcombustion for ammonia is 365 Btu/ft³. By comparison, the net heat ofcombustion for CO is 322 Btu/ft³.

The mixed ammonium salts formed according to the foregoing have a numberof uses. They may be sold “as is,” may be reprocessed to produce pureammonium sulfate, an item of commerce, or may be employed in a “limeboil” to recover the ammonia for reuse and render the sulfur benign. Inthe lime boil process, lime (CaO) reacts with ammonium salts at or nearthe boiling temperature of water (e.g., about 80° C.) producing thecorresponding calcium salt. For example:CaO+(NH₄)₂S→CaS+2NH₃+H₂O   (13)After recovery of the ammonia for reuse, air can be used to oxidize thecalcium sulfide to calcium sulfate (gypsum), which can be used toproduce wallboard or can be safely discarded.

The ratio of steam to coal fed to the reactor has a linear relationshipwith the H₂:CO ratio of the synthesis gas extracted from the reactor andcan be used to control and adjust the H₂:CO ratio. The linearrelationship between the ratio of steam to coal and H₂:CO of the presentinvention are illustrated in FIG. 8. A change of 6.06 percent in theratio of steam to coal results in a 5 percent change in the H₂:CO ratio(for example, from 2.0 to 2.1). The steep slope (about 40 degrees)between these two linearly related parameters allows one ratio, thesteam-carbon ratio, to be used to establish the other, the target H₂:COratio. According to one embodiment of the present invention, the massratio of steam to coal fed to the reactor is at least about 0.5:1, morepreferably is at least about 1:1 and even more preferably is at leastabout 2:1.

It is a particular advantage of the present invention that the synthesisgas extracted from the reactor has a controlled molar ratio of hydrogento carbon monoxide (H₂:CO) Without requiring additional steps for theremoval of carbon oxides to adjust the ratio prior to the synthesis ofuseful products such as methanol or methane. Accordingly, it ispreferred that the molar ratio of H₂:CO in the gas stream extracted fromthe reactor is at least 1:1 and more preferably is at least about 1.5:1.In particular, the synthesis gas can be extracted from the reactor andprovided to a methanol production step with a H₂:CO molar ratio of atleast about 2:1 (theoretical stoichiometric requirement), moreparticularly about 2.1:1 (the preferred requirement established bypractice). The synthesis gas provided to a methane production step canbe controlled to have a H₂:CO molar ratio of at least about 3:1, thetheoretical stoichiometric requirement. Thus, according to oneembodiment, the gas stream extracted from the reactor has a H₂:CO molarratio of from about 2:1 to 3:1.

After production of the synthesis gas, it can be converted to ahydrocarbon compound having either a gaseous, liquid or solid form.According to one preferred embodiment of the present invention, thesynthesis gas is converted to methane. Methods for converting synthesisgas to methane are known to those skilled in the art. Typically, thesynthesis gas is contacted with a catalyst at an elevated temperature.The catalysts can be, for example, nickel or molybdenum based catalystssupported on a carrier such as alumina. Examples of methanationcatalysts and reaction conditions are illustrated in U.S. Pat. No.4,540,714 by Pedersen et al., U.S. Pat. No. 4,525,482 by Ohaski et al.and U.S. Pat. No. 4,130,575 by Jorn. Each of the foregoing U.S. patentsis incorporated herein by reference in its entirety.

The methane formed from the synthesis gas can be burned directly in acombined cycle generator to produce electricity. Although the synthesisgas can be burned directly, it is generally more economical to convertthe synthesis gas to methane.

Methods of converting synthesis gas to methanol are known in the art andinvolve the contact of the synthesis gas, under pressure, with catalystssuch as copper/zinc/chromium oxide. Examples of processes for convertingsynthesis gas to methanol and other alcohols are disclosed in U.S. Pat.No. 4,348,487 by Goldstein et al., U.S. Pat. No. 4,843,101 by Klier etal, U.S. Pat. No. 5,703,133 by Vanderspurt et al., and U.S. Pat. No.6,248,796 by Jackson et al., which are incorporated herein by referencein their entirety. Synthesis gas can also be converted to syntheticcrude using known Fischer-Tropsch processes.

To conserve heat it may be desirable to keep the synthesis gas streamexiting baghouse at its elevated temperature (400° C. to 500° C.) priorto its being converted into methanol or methane. To do so, anhydrousammonia may be injected into the gas stream to react with the acid gascomponents producing ammonium sulfide ((NH₄)₂S), ammonium chloride(NH₄Cl) and ammonium fluoride (NH₄F). The ammonium salts that areproduced may be removed from the gas stream, for example by pulsedceramic filters. Thereafter, the purified gas stream can proceeddirectly to a conversion step without significant reheating.

In accordance with an alternative embodiment of the present invention, aprecursor gas composition can be formed in a reactor that can beconverted to ammonia (NH₄). According to this embodiment, steamintroduced into a reactor containing a reactive metal to form hydrogen,substantially as is described above. In addition, air or another gascontaining nitrogen and oxygen is introduced into the reactor such thatthe gas extracted from the reactor has a molar ratio of H₂:N₂ of about3:1 for the production of ammonia. The overall reaction is illustratedby Equation 14:12H₂O+(4N₂+O₂)+14Fe→14FeO+12H₂+4N₂ (14)

Control over the ratio of steam to air that is input to the reactor canbe used to control the ratio of hydrogen to nitrogen and so that thecomplete combustion of oxygen from air will provide sufficient heat forisothermally balancing the chemical (iron oxidation by steam) andenvironmental heat losses incurred in the reactor.

In a typical ammonia production method, a gas including hydrogen andnitrogen is compressed to about 200 atmospheres of pressure and passedover an iron catalyst at a temperature of from about 380° C. to about450° C. The production of ammonia from hydrogen and nitrogen isillustrated in: U.S. Pat. No. 4,600,571 by McCarroll et al.; U.S. Pat.No. 4,298,588 by Pinto; and U.S. Pat. No. 4,088,740 by Gaines. Each ofthe foregoing U.S. patents is incorporated herein by reference in theirentirety.

The resulting ammonia can be used in a number of applications. Forexample, the ammonia can be converted to urea for use in fertilizers.The ammonia can also be used to reduce NO_(x) emissions from coal-firedpower plants and for the manufacture of various ammonium-containingcompounds.

It is particularly noteworthy in accordance with the foregoingdescription that essentially the same plant equipment can be utilized toproduce different gas streams (e.g., hydrogen gas, sythesis gas or anammonia precursor gas) by simply changing the reactants that areadmitted to the reactor that is converting the reactive metal to a metaloxide. Thus, a single plant can readily produce a variety of valuablegas streams and the type of gas stream can be switched rapidly.

EXAMPLES Example 1

In this Example 1, a synthesis gas with a target molar H₂:CO ratio ofabout 2:1 was produced. This is the H₂:CO ratio that is required to makemethanol.

A reactor was fabricated using an alumina closed-ended tube (2″ ID×19″long) placed inside a stainless steel, closed-ended three-inch diameterpipe. The open end of the pipe was sealed with a flange. A one-inchexhaust line was provided to carry the synthesis gas from the reactorthrough a port on the flange. After exiting the reactor, the synthesisgas proceeded through a water-chilled condenser. Immediately afterexiting the condenser, the synthesis gas was sampled using TEDLAR bags.The synthesis gas proceeded through an ice-chilled condenser, where itwas scrubbed of particulates. Finally, the synthesis gas entered afloating drum, where the volumetric flow was measured.

A ½″ OD stainless steel lance was inserted through a second port in theflange and extended into the reactor. A flow of either steam or inertgas could be injected into the reactor through the lance. Coal wasinjected into the steam flow, thereby using the steam to carry the coalinto the reactor.

The reactor was charged with 0.7 kg of tin metal and 0.7 kg of ironpowder and heated to 1200° C. Ten grams of coal were loaded into aseries of valves attached to the lance and adapted to inject the coalinto the steam flow. A total of five individual charges of coal (2 gramseach) were injected into the flow of steam. Analysis of the coal isshown in the Table 4 below. TABLE 4 Coal Analysis Component PercentageCarbon 74.48% Hydrogen 5.34% Oxygen 8.85% Nitrogen 1.31% Sulfur 1.95%Ash 8.07% Total 100.00%

The total heating value of the coal was about 13,496 Btu/lb. The heatedreactor was purged using a flow of helium through the lance at 1.25standard liters/minute (slpm). The lance was not in contact with themolten bath at this time. Helium flow was terminated, the lance wasinserted in the molten bath, and steam was injected through the lanceinto the molten bath at 7.5 slpm. Hydrogen gas was produced for fourminutes by the reaction of steam oxidizing iron in the bath.

After four minutes, coal was injected into the steam lance, therebyinjecting both coal and steam into the molten bath. The coal wasinjected at 1.33 g/min by injecting 2 grams of coal into the steam lineevery 1.5 minutes. In off-reactor tests, the coal was observed tocontinuously eject from the bottom of the lance during this 1.5-minutetime frame at the steam rate used in this experiment.

Fifteen to thirty seconds after each injection, a ½ liter synthesis gassample was taken using a TEDLAR bag and the sample was analyzed usinggas chromatography at a later time. The average gas composition is shownbelow in Table 5. TABLE 5 Synthesis Gas Composition Synthesis GasAverage Composition Component (vol. %) Hydrogen 60.2 Carbon Monoxide26.5 Carbon Dioxide 11.2 Methane 2.1 Total 100.0

The H₂:CO molar ratio calculated from the above data is 2.27:1, slightlyabove the 2:1 target. The flow of synthesis gas from the reactor was4.75 liters/minute, calculated by measuring the change in gas volume inthe exhaust collection drum over time.

Example 2

10 grams of coal were injected with steam into a molten tin-iron bath(50 wt. % tin and 50 wt. % iron) having a temperature of 1200° C. Thesteam flow rate was 1.5 lbs/hr (14 l/min at standard conditions, 70l/min at tubing) and the coal was injected in 2 gram charges, 5 chargestotal (10 grams) at a rate of 1 charge every 1-2 minutes.

After injecting steam for 7 minutes into the molten metal (to stabilizeH₂ production), coal was fed into the reactor in 2-gram charges. Thecoal and steam were then injected into the molten metal through thelance. A new charge of coal was fed into the line every 1.5 to 2minutes. In this manner, from the initial charge, 10 grams of coal werefed into the reactor over 6.5 minutes. Gas chromatograph samples weretaken of the exhaust gas flow 10 to 30 seconds after each charge wasinjected. On average, a gas flow of 6.7 liters/min was obtained.Previously, a blank run of 1.5 lb/hr of steam by itself through theprocess created 2.2 liters/min of hydrogen (no tin, iron or coal in theprocess). Therefore, it was calculated that 4.5 liter/min of gas wasproduced from the reactions of the steam and coal in the tin/iron melt.

Of the 4.5 liter/min of gas, the average gas composition was measuredand the results are illustrated in Table 6. TABLE 6 Synthesis GasComposition Quantity Gas Component (vol. %) H₂ 66.2 CO 18.1 CH₄ 3.5 CO₂12.1

As is illustrated in Table 6, the gas composition had an average H₂:COmolar ratio of 3.66:1.

If the data from Example 1 and Example 2 are extrapolated, it ispossible to project that a steam flow requirement of about 6.24 standardliters/min is necessary to produce a 2:1 (H₂:CO) ratio for theproduction of methanol.

Example 3

The following Example 3 is an evaluation of a process for making syngassuitable for methanol synthesis that was performed using METSIM, acomputer program for complex chemical, metallurgical and environmentalprocesses available from Proware, Tucson, Ariz.

The carbonaceous material was coal from Ohio (Ohio #6, Carroll County,Ohio) with ASTM rank hvBb. The analysis of the coal is summarized inTable 7. TABLE 7 Analysis of Ohio #6 Coal Proximate Analysis Moisture5.25 (%, As Received) Volatile Matter 37.19 Fixed Carbon 48.19 Ash 9.37Total 100.00 Heating Value 12,388 (Btu/lb As Received) Ultimate AnalysisCarbon 71.95 (%, Dry) Hydrogen 5.10 Oxygen 7.77 Nitrogen 1.43 Sulfur3.86 Chlorine Not reported Fluorine Not reported Phosphorous Notreported Ash 9.89 Total 100.00 Sulfur Forms Pyritic 2.26 (%, Dry)Sulfate 0.12 Organic 1.48 Total 3.86

FIG. 9 illustrates the material balance that can be achieved using ironas the reactive metal in the synthesis gas reactor at a temperaturevarying from 1200° C. to 1300° C. Specifically, the coal was fed to apyrolyzer (750° C.) at a rate of 47.75 tons/hr with oxygen (2.61tons/hr) and steam at 1000° C. (38.65 tons/hr). The volatiles, steam, COand N₂ are transferred to the synthesis gas reactor and the fixed carbonand ash are transferred to the FeO reduction reactor. The resulting gascomposition extracted from the synthesis gas reactor included hydrogenat 5.33 tons/hour and carbon monoxide at a rate of 35.27 tons/hr, for aH₂:CO molar ratio of about 2.1:1, which is ideal for conversion tomethanol.

While various embodiments of the present invention have been describedin detail, it is apparent that modifications and adaptations of thoseembodiments will occur to those skilled in the art. However, it is to beexpressly understood that such modifications and adaptations are withinthe spirit and scope of the present invention.

1. A method for the production of a gas stream comprising H₂ and COcomprising the steps of: a) providing a molten metal in a reactorcomprising at least a first reactive metal; b) contacting steam withsaid molten metal to react a first portion of said steam with saidreactive metal to form hydrogen gas and a metal oxide; c) contacting acarbonaceous material with said molten metal in the presence of steam toreact said carbonaceous material with a second portion of said steam andform carbon monoxide gas; and d) extracting said gas stream from saidreactor.
 2. (canceled)
 3. A method as recited in claim 1, wherein saidreactive metal is iron.
 4. A method as recited in claim 1, wherein saidreactive metal is tin. 5-8. (canceled)
 9. A method as recited in claim1, wherein said gas stream extracted from said reactor comprises atleast about 50 volume percent hydrogen gas.
 10. A method as recited inclaim 1, wherein said gas stream comprises not greater than about 15vol. % carbon dioxide.
 11. A method as recited in claim 1, wherein saidgas stream comprises a molar H₂:CO ratio of at least about 1.5:1.
 12. Amethod as recited in claim 1, wherein said gas stream comprises a molarH₂:CO ratio of at least about 2:1.
 13. A method as recited in claim 1,wherein said gas stream comprises a molar H₂:CO ratio of from about 1:1to about 3:1. 14-15. (canceled)
 16. A method as recited in claim 1,further comprising the step of contacting an oxygen-containing gas withsaid molten metal.
 17. A method as recited in claim 1, wherein saidsteps of contacting steam and contacting a carbonaceous materialcomprise the step of injecting said carbonaceous material entrained insaid steam into said molten metal.
 18. A method as recited in claim 1,further comprising the steps of: e) terminating said contacting ofsteam; and f) contacting said metal oxide with a reductant to reducesaid metal oxide back to said molten metal.
 19. A method as recited inclaim 18, wherein said reductant comprises a particulate carbonaceousmaterial.
 20. A method as recited in claim 18, wherein said reductantcomprises particulate coal.
 21. (canceled)
 22. A method as recited inclaim 1, further comprising the step of adding a flux to said moltenmetal to promote the formation of a slag layer over said molten metal.23. A method as recited in claim 1, wherein said carbonaceous materialcomprises a material selected from the group consisting of municipalwaste, hazardous waste and petroleum coke.
 24. A method as recited inclaim 1, wherein said carbonaceous material comprises municipal waste.25. (canceled)
 26. A method as recited in claim 1, wherein the massratio of steam to carbonaceous material is at least about 0.5:1. 27-110.(canceled)